The performance of a wireless transceiver relies heavily on the performance, e.g., linearity, efficiency, etc., of the amplifiers used by the wireless transceiver to amplify signals, e.g., for subsequent transmission. To achieve good power efficiency and linearity, a power amplifier may comprise a plurality of amplifier cells that each operate as B-class amplifiers. For example, the input bias point for each amplifier cell is typically set close to the amplifier cut-off to achieve a high linearity across the entire input voltage range characteristic of B-class operation. Typical B-class amplifier cells, however, are sensitive to process variations. For example, process variations incurred during the manufacture of the amplifier cells cause large gain step variations between amplifier cells, especially when operating with low gain levels (e.g., due to a small input signal and/or due to the power amplifier having only a small number of active amplifier cells.
Conventional solutions to this problem may adjust, for example, the bias point of the active power amplifier cells such that they operate as an A-class amplifier when operating with low gain levels. In so doing, the conventional solution improves the linearity of the power amplifier for these low gain level situations. However, because A-class power amplifiers are significantly less efficient than B-class power amplifiers, this conventional solution increases the already problematic efficiency problems.
Thus, there remains a need for improved power amplifier solutions that achieve a desired linearity and efficiency even when operating with low gain levels.